The Core normally provides diagnosis and care to a large number of patients with Alzheimer's disease (AD), and can provide a pool of thoroughly evaluated AD patients and controls for clinical investigation and autopsy studies. These subjects will be utilized in this Program Project for studies of peripheral endocrine and calcium regulation and a therapeutic trial in Project 5, and autopsy tissue will be utilized in Projects 1 and 2 of the program project proposal. Periodic reassessment of the cognitive capabilities of the patients, their level of independent functioning, and the relative rates of their functional decline offer a seminal opportunity for correlative clinical-pathological-neurochemical studies. All quantitative data on patients will be kept in a computer designed for storage, search and retrieval of clinical information. In addition, patients in the mild to moderate stage of "probable" AD will be recruited for the Calcitriol (1,25(OH)2D) study in Project 5. These patients will have a gradually progressive intellectual decline, have a Mini-Mental State Exam score between 24 and 12, a mild to moderate rating on the Alzheimer's Disease Assessment Scale and the Dementia Rating Scale and a Clinical Dementia Rating of 1 or 2 (moderate). Other criteria for inclusion in the Calcitriol study are outlined in Project 5 of the program project proposal.